Any part of the electromagnetic spectrum has a frequency that decides what type of wave it is. This frequency does not change when the wave is refracted. If the speed of the wave is reduced the wavelength of the wave must therefore also be reduced as:

Speed = frequency x wavelength

So the wavelength of blue light in air will be slightly longer than the wavelength of blue light in glass!

So we know that waves slow down when they enter optically denser materials, and bend towards the normal line.

But can we predict how far waves will change direction?

If we label the angle of incidence as i and the angle of refraction as r, then it can be shown that when travelling from a vacuum into a material, the ratio
remains constant for all values of i and r. This is Snell's Law.